Field of the Invention
In many machines, devices, and arrangements with oscillating masses measures have to be taken to prevent, or at least keep within very narrow limits, the transfer of oscillations to other components of the machine. Although in the case of periodic oscillations the spring-mass system can be designed in such a manner that the resonance frequencies are as far apart as possible from each other, thereby preventing masses or mass systems capable of oscillating from resonating as a result of the natural frequency of the oscillating mass, such a measure is insufficient to prevent undesirable oscillations of other components or groups of components. Apart from this, it is ineffective in the case of systems with varying resonance frequencies.
Measures for damping oscillations are widely known. In many instances, however, it is very difficult to dampen an oscillating structure or such damping is undesirable deisrable because it would impair the function of the oscillating system. Therefore, the measures taken to this end were frequently aimed at damping, by means of flexible resilient elements, a transfer of oscillations between components mechanically coupled to each other. However, in most cases such measures change merely the characteristic of the spurious forces, such as jerks or vibrations of adjacent machine components, without a significant reduction being obtained in the amount of energy transferred.
Oscillation quenching, also known as dynamic absorption, has proved the most effective method of preventing an undesirable transfer of oscillation forces of moved masses. This method ensures that the forces transferred to adjacent machine components are compensated at least in part and that in principle it is possible for oscillations to be quenched completely. The overwhelming majority of the known oscillation quenching arrangements relate to freely oscillating structures, whose oscillations are solely a function of the dimensions of the oscillating structure, such as overhead lines, for which an oscillation quenching arrangement is described in published West Germany Pat. application No. 2,056,164. Also known, however, are oscillation quenchers for constrained or forced oscillations, i.e., oscillations encountered in connection with masses capable of oscillating and which are moved by an extraneous -- periodic or aperiodic -- driving power. One of the most significant solutions in this field is what is known as the Taylor pendulum which for quenching constrained rotary oscillations on motors becomes effective over the full speed range. The Taylor pendulum is a rotating system with an eccentrically coupled centrifugal pendulum, whereby the excitation is diverted from the actual oscillating system to the coupled pendulum. See VDI-Zeitschrift, Nov. 5, 1938, pages 1297-1300. The disadvantages of this solution are that an additional oscillating mass is needed and that the pendulum can be used only for rotating mass systems.
Also see K. N. Tong's "Theory of Mechanical Vibrations" pages 138, through 146, J. Wiley & Sons, 1960, which discusses dynamic vibration absorbers consisting of a small vibratory system coupled to a machine, or other structure, to control vibrations. Such an absorber is designed so that when the machine is subject to a periodic oscillatory excitation the resulting vibration produces coupling forces that tend to cancel out the excitation forces.
West German Pat. No. 1,030,594 published on May 22, 1958, discloses a mechanical vibration system whose active mass carries at least one electromagnetic vibration generator joined to it by a coupling spring. The coupling spring and the total mass of the generator are dimensioned in such a manner that the natural frequency of the oscillation system equals, or almost equals the operation frequency.
Another prior art arrangement is shown in Hartmann's West German patent application No. 1,806,110 published on June 12, 1969 with priority of first filing in the United States on Nov. 2, 1967. This arrangement is a two mass vibration system consisting of a funnel, material being transported through the funnel to a material receiving transport tray for receiving a controlled quantity of material per unit of time such that the masses are flexibly coupled to form a correlated system having a single degree of freedom and whose mass natural frequency is nearly the same as the excitation frequency.
Also known, however, is an oscillation quencher which is used for linearly oscillating spring-mass systems. In this quencher which is known as the Frahm quencher (see Den Hartog, "Mechanical Oscillations," McGraw Hill 1934, p. 104) an oscillation system which is small in relation to the oscillating machine component is coupled to the main system whose natural frequency .sqroot.c/m is chosen so that it equals the oscillating or excitation force. However, this arrangement, too, requires an additional oscillating mass and has the disadvantage that oscillations can be quenched only in those cases where the frequency of the excitation force is essentially constant. Therefore, the use of the latter system is limited to apparatus which is directly coupled to electric synchronous motors or synchronous generators.